The invention relates to a steering device for motor vehicles with a steering shaft.
Steering devices for motor vehicles are frequently implemented in two parts, one slidable into the other. In the event of a frontal collision the steering device does not endanger the driver because the steering device yields upon impact of the body onto the steering wheel and the impact energy is absorbed. In known devices, the slidable steering shaft tube, which receives the control wheel-side steering shaft, is disposed in a casing which is clamped with respect to the motor vehicle chassis by machine screw fastening in a predetermined position. The machine screw fastening is herein implemented such that upon impact, the steering wheel side shaft end with an axially directed and machine screwed casing bracket, is movable along a specific path. The impact energy is correspondingly absorbed by the machine screwed clamping. In order to make the energy absorption more uniform in the event of impact, additional energy absorption elements are disposed between the longitudinally slidable shaft and the chassis of the motor vehicle. An energy absorption element, which is implemented as a sheet metal tongue that can be torn away, is, for example, known in the art from GB 1,390,889.
One disadvantage of known crash systems for steering columns is that the break-free force cannot be defined over wide ranges independent of the energy absorption force. Also, the absorption behavior cannot be reproducibly preset.
The object of the present invention is to provide a crash system for a steering column configuration, which eliminates the disadvantages of the prior art. In particular, the object is to provide a crash system for steering columns which permits a break-free force and a defined energy absorption with reproducible behavior. In addition, the steering column configuration is simply mounted and cost effective.
Accordingly, a steering shaft is supported in a guide box which, in turn, is fixed to a retaining bracket. The retaining bracket comprises laterally flange-like slide faces which are clamped tightly on the motor vehicle chassis via machine screws. The clamping is implemented in such a manner that in the event of a crash, the steering shaft, along with the bracket, can be displaced by several centimeters.
An energy absorption element is stationarily connected to the chassis. The absorption element is preferably a sheet metal part with a tear-away flap, mounted between the bracket flange and the chassis. The attachment of the steering column configuration to the chassis is possible using preferably two machine screws. This provides for a rapid, cost-effective mounting.
The steering column configuration is implemented such that in the event of an impact, the break-free force is separated from the energy absorption force upon sliding of the steering shaft. A clamped break-free element is released immediately to dissipate the impact energy. As a result, the energy absorption over a defined displacement path is not substantially affected by undefined clamping forces and the absorption effect is predetermined through the implementation of the absorption element.
The casing bracket and stationary chassis have facing portions which are pressed together by clamping elements. The facing portions are slightly inclined at a specific wedge angle with respect to a sliding direction. The original clamping is immediately reduced because the two wedge face parts move apart according to the angular slope. In case of an impact the clamping is already broken after a displacement of a few tenths of a millimeter and the further displacement is no longer determined by undefined clamping forces. The casing bracket, which is fixed to the steering shaft tube, is also connected to the chassis via a tearaway strip. The implementation of this tear-away strip determines the degree and the time course of the energy absorption behavior. The energy absorption behavior can be optimized for a more gentle interaction with the driver by adjustment of the dimensions of the tear-away flap.